Why not just download the SD version and copy it manually to the SD card.
Size of map is only 188 MB

You can still use your Mapsource version to make tracks and sent it to the Etrex.

I just tested with the Bulgaria map in Mapsource and the track install on the Etrex with no problems at all.

Spoiler: Here is the SD version of Topo Bulgaria
Code:
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